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Scientific Value of Arctic Sea Ice Imagery Derived Products 3 Recommendations Recommendation: The intelligence community should release and disseminate all Arctic sea ice Literal Imagery Products (LIDPs) that have been produced to date as soon as possible. As detailed in the previous chapters, great immediate benefits can be derived from the release of all Arctic sea-ice LIDPs because they will help improve our understanding of important climate-system processes and add substantial value to other remote-sensing and modeling efforts. The images provide information at scales, locations, and time periods that are extraordinarily important in advancing our knowledge of critical processes during this period of rapid loss and transformation of Arctic sea ice. There are no other data available that show the melting and freezing processes that we were able to observe in these images. Their release will have a major impact on understanding effects of climate change on sea ice and ice habitat. DISSEMINATION PRIORITIES All of the Arctic sea ice LIDPs contain information that will be extremely valuable to scientific research. Three categories of LIDPs are of particularly high priority for dissemination and publicity efforts: (1) all six sites during 2007-2008, (2) all from the Barrow site, and (3) all from the Beaufort Sea site. 2007-2008 Images Placing a high priority on the publicity of the availability of images from all six sites during 2007 and 2008 is critical, because this window coincides with the research programs undertaken during International Polar Year (IPY). The availability of 2007-2008 images will greatly enhance the benefits and value of a broad range of intensive ground-based observations that were collected during the Fourth IPY. Furthermore, this subset of the data includes images of the summer 2007 minimum in sea-ice coverage, a record low that was more than 20 percent below the previous low (in 2005) and nearly 40 percent below the 1979-2000 average minimum (Figure 1.4, Stroeve et al., 2008). This dramatic loss of sea ice will be investigated in more detail using this high-resolution imagery.
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Scientific Value of Arctic Sea Ice Imagery Derived Products Barrow Giving high priority to the dissemination of all LIDPs from the Barrow site would support a range of high-profile research projects in the coastal region at Barrow (Norton, 2001). These data will serve as an important resource for questions revolving around adaptation of coastal communities and ecosystems to climate change (see Figures 1.1, 3.1). FIGURE 3.1 LIDP over Barrow Fiducial Site acquired on 18 June 2006. The two boxes shown in (a) are approximately 400 m to the side and are shown at a scale that approaches the limit of resolution at right. For the patch of highly deformed ice shown in (b) the approximately 1-m pixel dimensions are sufficient to partly resolve the block structure in the pressure ridges (broken ice piled to several meters thickness or more). Such deformed ice areas serve as important habitat for seals and polar bears. These deformed ice areas may help anchor the coastal landfast ice shown here, thereby creating a platform for animals and people. They can also represent a significant obstacle to subsistence hunters who construct seasonal trails on the landfast ice at Barrow. Note the contrast in the distribution of surface melt ponds in the deformed ice as opposed to flat ice shown in (c). The degree of ice deformation and its surface roughness are important in controlling the lateral extent and depth of melt ponds and hence ice albedo. SOURCE: Figure courtesy of USGS National Civil Applications Program.
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Scientific Value of Arctic Sea Ice Imagery Derived Products Beaufort Sea The Beaufort Sea, with imagery dating to 1999, has seen some of the most substantial rates of sea-ice thinning and retreat anywhere in the Arctic (Serreze et al., 2007). It also exhibits the broadest range of different ice types and ice ages, greatly increasing the value of Arctic sea-ice LIDPs in improving our ability to monitor the movement and evolution of different ice age and thickness classes. At the same time, converging economic activities (natural resource extraction and shipping) and indigenous interests (subsistence harvest of marine mammals) in the Beaufort region place great importance on the detection and tracking of multiyear ice. Such ice represents both an important resource for coastal communities and ecosystems (e.g., as a platform and habitat) as well as a potential hazard for industrial activity (Eicken et al., 2009). Forecasts of regional sea-ice conditions on seasonal timescales can help different stakeholders prepare for and adapt to the impacts of climate change and minimize environmental risks associated with industrial activity. However, the most promising approaches for forecasts on these timescales (Drobot and Maslanik, 2002; Zhang et al., 2008) require much better information on relationships between ice age, thickness, and surface-melt than are currently available. Placing a high priority on the dissemination of LIDPs from the Beaufort site for all available years would be of great value. Increasing ship traffic and offshore oil and gas exploration activities in this region would also benefit from more accurate determination of the ice edge and hazardous ice conditions through validation of other satellite remote-sensing data sets such as the Special Sensor Microwave Imager (SSM/I) and Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) with LIDPs. Recommendation: To maximize the utility of the images, the committee recommends that the metadata include: thumbnail (smaller size) copies of the images, exact information on the location of the images, calibration information, the time of acquisition, and information on the pointing angle. Metadata (additional information that accompanies the actual data) is a critical part of a data set that can significantly enhance its general and broader usefulness. The committee understands that the trustees of the fiducials archive, the U.S. Geological Survey’s Civil Applications Program, are preparing a website to disseminate the derived Arctic sea-ice images. Inclusion of these metadata in the online archive would greatly facilitate the research of scientists who obtain the images. For the data set in question the following would be the most useful: Thumbnail (smaller size) copies of the images. The raw images are rather large and copies of the images with reduced resolution will make browsing through the catalogue much easier. Exact information on the location of the images. The data are already mapped to a standard projection and resolution. As pixel size is known, only the latitude and longitude of the center are needed. If possible, calibration information would be very useful. This would allow the scientists to intercompare the data sets. For example, with increasing sea ice melt, the ice and snow gets darker (the albedo is decreasing). Calibration would
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Scientific Value of Arctic Sea Ice Imagery Derived Products enable scientists to estimate the rate of this darkening which would lead to a better understanding the melt process. The time acquisition (the nearest hour should be sufficient). At this high resolution, ice drift within hours can make a difference. This needs to be accounted for when the data set is compared with other data sets, which could be data from civilian satellites, aircraft data, or in-situ measurements. The time is also important for the estimation of the sun angle. If possible, information on the pointing angle would be very valuable. Together with calibration information and the sun angle (determined from the time of the acquisition), we can then calculate an objective brightness of the sea ice, which makes it tremendously easier to intercompare the data and investigate the temporal evolution of the sea ice. The pointing angle would also be useful in accounting for any distortion in the data. CONSIDERATIONS FOR THE FUTURE If data will be collected in the future and LIDPs produced for the purpose of public release, some modifications/additions would make the data even more useful for scientific research. Operators of national assets could continue collecting ice images during suitable atmospheric conditions at the existing Beaufort Sea, Canada Basin, and Chukchi Sea sites. Assuming that the location and number of sites is not fixed, adding collection of imagery at the North Pole, where extended field observations are already underway, would be particularly valuable. Dynamic image collection that tracks how individual ice features evolve over time and a mechanism to communicate this information in near real-time for a given feature would complement the existing data, which are images at fixed locations in space through which different ice features pass over time. In 1999, when Medea scientists requested the collections at the original four sites in the Arctic Ocean shown in Figure 2.1, it was known that viewing the ice repeatedly at fixed coordinates was not ideal because, due to the movement of the ice, the satellite would view different ensembles of floes every time a picture was taken. To derive most information about the physical processes occurring in the snow ice system–including meltpond evolution—will be necessary to view the SAME ensemble of floes as it drifts along under the influence of winds and ocean currents. This will require that these ensembles are identified by their surface characteristics, or marked by a data buoy that records its position via the Global Positioning Systems. When the Medea scientists made the initial request, it was not clear whether the unclassified systems would be able to provide the necessary continuous records and what agency would take responsibility to communicate daily coordinates of the ice to the intelligence community. However, near-real time locations of the selected ensembles of ice floes can be derived from unclassified SAR and Ice, Clouds, Land Elevation Satellite (ICESat) systems, or by the International Arctic Data Buoy Program. Those data could be used for location determination. Furthermore, several scientists calculate sea ice drift from satellite active and passive microwave data, which most likely could also be used to follow specific sea ice floes. If corresponding radar data exist, it would be outstanding if those data could be made available as well. They would not only help us with the filling data gaps in times of cloudiness, but the different physical principle of radar remote sensing compared to visible remote sensing would yield additional information about the characteristics of the sea ice. For example, radar responds more strongly to wetness and sea ice roughness.
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Scientific Value of Arctic Sea Ice Imagery Derived Products Because of the large contrast between open water and ice, visible images can at times be saturated for the generally white sea ice. Nevertheless, there is valuable information in those “different shades of white.” For example, as snow and ice age they get slightly darker. Also variations in surface topography can be identified. Therefore, data with the full dynamic range in contrast would be preferable. Any Multi-spectral data, if available, would be particularly valuable to obtain more complete information on albedo and radiative surface fluxes.